The present invention relates to die casting of a molten metallic material in a shot sleeve.
Sputtering is a commonly used deposition process to deposit a coating on a substrate. In a typical sputtering process, a target is impinged with high energy electrons or other atomic particles to dislodge material from the target for deposition on the substrate. Certain sputter targets contain a significant weight fraction of one or more precious and/or expensive metals. As a result, raw material costs are a substantial proportion of the final product (target) cost. In the past, disk-shaped sputter targets have been made using powder metallurgical and wrought metal fabrication processes.
U.S. Pat. No. 6,070,643 describes a vacuum die casting apparatus and method especially useful for die casting reactive metals and alloys.
The present invention provides a method for making a cast product using a die casting method wherein a molten metallic material is introduced into a shot sleeve having an end that is closed by a relative movement between a closure member and the shot sleeve. The molten metallic material is forced by movement of a plunger in the shot sleeve to the closed end of the shot sleeve where the plunger maintains pressure on the metallic material until it is at least partially solidified in the shot sleeve in the form of a cast product shape having a outer peripheral shape corresponding to the inner peripheral shape of the shot sleeve. The end of the shot sleeve then is opened by relative movement between the closure member and the shot sleeve, and the plunger is moved further to eject the cast product from the open end of the shot sleeve. The invention is useful, although not limited to, making disk-shaped cast sputter targets.
In an illustrative embodiment of the invention, the metallic material is melted under subambient pressure (relative vacuum) that is also provided in the shot sleeve. In another illustrative embodiment of the invention, a plug is placed in front of and axially spaced from the plunger in the shot sleeve, and the molten metallic material is introduced between the plunger and the plug. The plunger is moved in the shot sleeve so that the plug abuts the closure member and so that the molten metallic material can solidify between the plunger and the plug. The plug can be configured to impart a desired shape to an end face of the cast product which contacts the plug. The plunger tip can be appropriately configured to impart a desired shape to an end face of the cast product which contacts the plunger tip.
The present invention is advantageous to conserve the metallic material since no disposable gating and runner systems are needed which are filled with the metallic material. The molten metallic material is solidified in the shot sleeve, eliminating the need for machined die set having a die cavity. The use of plunger pressure on the solidifying metallic material in the shot sleeve reduces shrinkage porosity that may occur as the molten metallic material solidifies. The invention can produce net or near net shape die cast components having an outer periphery corresponding to the inner periphery of the shot sleeve and one or more end faces or surfaces having a desired configuration.
Details of the present invention will become more readily apparent from the following detailed description taken with the following drawings.